Apparatus for treatment of soils contaminated with organic pollutants

ABSTRACT

An apparatus for treating soil contaminated by organic compounds wherein an ozone containing gas is treated with acid to increase the stability of the ozone in the soil environment and the treated ozone applied to the contaminated soil in a manner adapted to decompose the organic compounds; one embodiment of the apparatus comprises a means to supply ozone as a gas-ozone mixture, a stability means to treat ozone obtained from the supply and distribution means to apply the stabilized gas-ozone to soil. The soil may be treated in situ or may be removed for treatment and refilled.

This is a continuation in part of copending application(s) Ser. No.07/101,049 filed on Sep. 25, 1987, abandoned.

FIELD OF THE INVENTION

This invention relates to an apparatus for treating soil contaminatedwith organic compounds. The apparatus has utility in treating the soilin situ without having to remove the soil from the site. The treatmentresults in degradation of the organic compounds to less hazardouscompounds or compounds that are more readily biodegradable than theparent compound. The apparatus has particular utility in degradingorganic compounds comprising unsaturated aliphatics, some alkanes andaromatics, and some of their halogenated compounds.

BACKGROUND OF THE INVENTION

Ozone is an allotropic form of oxygen containing three oxygen atoms permolecule. It is an extremely powerful oxidizing agent with theoxidation-reduction potential being 2.7 volts. Ozone reacts with a largenumber of organic compounds in aqueous and nonaqueous environments.Since ozone decomposes rapidly, its application in the destruction oforganic waste is limited unless it is introduced continuously. Thestability of aqueous ozone, however, can be improved by several methodswhich include lowering the solution pH or increasing the concentrationof base in high pH environments. Ozone half-life values in 0.05 Mphosphate buffer solutions at pH 4 and 10 are approximately 10,000 and10 seconds, respectively. Hoigne and Bader; Hoigne, J., and Bader, H.,1983, Rate Constants of Reactions of Ozone with Organic and InorganicCompounds in Water-I, Water Research, Vol. 17, pp. 173-183; reportedthat the addition of sodium bicarbonate and dimethyl mercury increasedthe stability of ozone at high pH. An increase in base (NaOH)concentration from 1 N to 20 N also results in the extension of thehalf-life of ozone by more than three orders of magnitude. However, suchhigh base concentrations or application of chemicals such as methylmercury are not practical for on-site treatment of contaminated soil.

In most of the previous work, ozone has been used to destruct or treatorganic wastes present in aqueous media (U.S. Pat. Nos.: 2,703,247;3,920,547; 4,029,578; 4,076,617; 4,098,691; 4,487,699; 4,537,599;4,619,763; Japanese Patents: 4,500; 43,304). Application of aqueousozone solutions to treat contaminated soil is difficult because of therelatively slow liquid permeation through soils and rapid decompositionof ozone. For example, if aqueous ozone is applied at a 2-atm/m pressuregradient to a soil having a permeability of 0.1 m/day (e.g., clay-loamsoil), the liquid front will move only at a velocity of 0.16 m/hr.Because of these low flow velocities, practical value of aqueous ozonetreatment of contaminated soils is very limited.

According to Hazen-Poiseulle's approach, if the pressure gradient isconstant and the fluid compressibility is neglected, the velocity of aNewtonian fluid under capillary flow conditions is inverselyproportional to the dynamic viscosity of the fluid. Then, undercapillary flow conditions and ambient temperatures, air flow velocity isabout two orders of magnitude (100 times) faster than that of water. Theflow velocities of an ozone-oxygen or an ozone-air mixture are similarto air flow velocity. Because of rapid penetration, ozone gas, can beeffectively used in soil decontamination provided the gas phasereactions can be established with organics in soils. To the knowledge ofthe inventor, there are no studies on the application of ozone gas totreat soils contaminated with hazardous organic wastes. According to arecent report published by the U.S. Environmental Protection Agency;U.S. Environmental Protection Agency, 1985, Remedial Action at WasteDisposal Sites (Revised), EPA/625/6-85/006, Office of Emergency andRemedial Response, U.S. EPA, Washington, D.C. pp. 9-53; "Ozone is usedin the treatment of drinking water, municipal wastewater, and industrialwaste, but has never been used in the treatment of contaminated soils orgroundwater". This indicates that ozone, either in aqueous or gasphases, has not been used for soil decontamination. In the presentinvention, a pretreated gas-ozone mixture was used to decontaminatesoils containing hazardous organic wastes.

It is an object of the present invention to stabilize gaseous ozone inthe soil environment. It is a further object of the invention tostabilize the gaseous ozone in an efficient and cost effective manner. Afurther object of the invention is the efficient and expeditiousdecontamination of soil. Another object of the invention is to allow thein situ treatment of contaminated soil.

SUMMARY OF THE INVENTION

The invention provides a process and apparatus for the treatment of soilcontaminated with organic pollutants. The process includes the steps ofproviding a supply of a gas-ozone mixture, treating the gas-ozonemixture with acid in a manner to promote the stability of ozone in themixture, and applying the stabilized gas-ozone mixture to soilcontaminated with organic compounds that are susceptible to reactionwith ozone. The soil may be treated in situ or excavated and treated ina chamber. If in situ application is contemplated one or a plurality ofwells may be drilled in the contaminated soil and the gas-ozone mixtureinjected in the wells. A final neutralizing step may be included where aneutralizing chemical reacts with residual ozone remaining in the gasmixture prior to allowing the gas to vent to the atmosphere.

A general description of the apparatus useful for producing thestabilized gas-ozone mixture for treating soil contaminated withorganics includes at least an ozonator (ozone generators adapted toreceive an oxygen containing gas from a gas supply means, that generatesozone from oxygen in the gas to produce a gas-ozone mixture and ozonestabilizing means adapted to receive the gas-ozone mixture from theozone generator and stabilize the mixture by contacting the mixture withan acid to produce a stabilized gas-ozone mixture. In another embodimentthe apparatus may include gas supply means adapted to supply gascontaining oxygen to an ozone generator, and distribution means adaptedto receive the stabilized gas-ozone mixture and distribute the mixtureto the soil. Another embodiment may optionally include a gasconditioning means that purifies and/or pressurizes the gas prior totreatment in the ozonator. A further embodiment, may include gasneutralizing means for neutralizing residual ozone remaining in the gasafter soil treatment. A final embodiment includes distribution means foradvantageously applying the gas-ozone mixture to the soil. Thedistribution means may be designed for in situ treatment or fortreatment in a chamber where the excavated soil has been placed. Thedistribution means for in situ treatment includes drilled wells andassociated piping through which the gas-ozone mixture may be injectedinto the soil.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in block diagram form the major steps of theinvention.

FIG. 2 illustrates several embodiments of the invention useful indecontaminating soil.

FIG. 3 is a graph showing the destruction of an organic contaminant(phenol) according to the invention.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENT

The invention presented herein was discovered in the search for a soiltreatment technique. First, the low stability and rapid decomposition ofozone in the soil environment was observed. Second, since ozonedecomposes rapidly in soils, a method was developed to promote itsstability. This method involves the pretreatment of ozone gas.Pretreatment of ozone gas is preferred to soil treatment because theformer can be cost effective. Pretreated ozone was found to be capableof decontaminating soils containing hazardous organic wastes.

Referring to FIG. 1 that illustrates in block diagram form the essentialsteps of the invention. A source of gas, gas supply means 101, isrequired that contains oxygen. The gas may be from oxygen tanks, airtanks or the atmosphere. Depending on the source of the gas, the gas mayneed conditioning such as purification and pressurization. Purificationremoves constituents of the gas that may be harmful to the process orequipment. For example, if air is used moisture may need to be removedso that the ozonator 103 is not adversely affected. The gas may need tobe further pressurized to provide sufficient pressure and flow at theeventual point of distribution. Pressurization ahead of the ozonationunit is preferred to avoid ozone decomposition in the process ofpressurization. The use of conditioning means 102 is optional. Afterozonation the gas now containing ozone is treated in stabilizer 104 tostabilize the ozone by contacting the gas with acid. Finally, thestabilized gas-ozone mixture is distributed to soil contaminated withorganic pollutants by distribution means 105. Soils not saturated withwater, i.e. above the saturated zone, are contemplated for treatment bythe invention herein.

Referring now to FIG. 2. A source of gas, gas supply means 101, isrequired. The gas must contain oxygen and can be obtained from a tank110 or the atmosphere 111. The gas flows to a conditioning means 102 viavalved pipes 112, 113, and 114. On-off valving in the Drawing isdesignated as a circle labeled with a V. These may be arranged as neededto control gas flow. The conditioner optionally comprises a gas purifier120 and/or a pump 121.

The gas conditioning means 102 provides gas purification and/orpressurization to the levels needed by the subsequent equipment and toprovide proper flow. Gas purifier 120 removes unwanted materials fromthe gas (e.g., moisture and suspended matter such as dust) that wouldinterfere with subsequent processes. Pump 121 is useful when additionalgas pressure for distribution of treating gas to the soil is needed.After purification the gas flows by pipe 122 to three way valve 123 andthence to either pump 123 by pipe 124 or around the pump by pipe 125.

Thereafter, the gas flows to ozonator 103 by pipe 130. The ozonatorconverts a portion of the oxygen in the gas to ozone to obtain agas-ozone mixture. The higher the oxygen concentration of the gas thegreater the ozone concentration that is obtained and the faster the soiltreatment. The gas used in the experiments herein was over 99.9 percentoxygen, yet resulted in only a small amount of ozone formed as discussedlater. A high ozone concentration is preferred; however, economics maydictate that air be the starting material rather than oxygen.

The gas-ozone mixture flows from ozonator 103 by pipe 131 to the ozonestabilizer means 104. The stabilizer means 104 may comprise a containerwith a spray system or a like device that can contact acid with thegas-ozone mixture in a manner to stabilize the mixture. Alternatively,bubbling the gas-ozone mixture through acid is another way to contactthe acid. FIG. 2 shows the actual embodiment used in the tests for thestabilizer 104. The embodiment comprises an isolation container 140coupled to an acid container 142 by pipe 141. The acid container 142 isthen coupled to another isolation container 144 by pipe 143. Thefunction of the isolation containers 140, 144 is to prevent acid fromspilling into pipe 131 or pipe 149. Acid 146 in container 142 may be anyacid capable of stabilizing the ozone to an acceptable level. Presentlythe preferred acid useful in this invention is nitric acid because ofits relatively high vapor pressure. Other strong acids such as sulfuricand hydrochloric may be used as long as they do not produce harmfulby-products after reacting with organics in soils. Whether diluted (withwater) or undiluted the acids must be present at a concentration thatprovides sufficient protons for ozone stabilization. The concentrationis generally sufficient at a pH of about one (1) or less. Stronginorganic acids are preferred.

The term stabilized gas-ozone mixture includes an oxygen-ozone mixture,air-ozone mixture, and ozone mixed with other gases that are expeditiousin the method of the present invention and have been treated by contactwith an acid so as to increase the stability of the ozone in the gaswhen contacted with soil.

After stabilization in stabilizer 104 the stabilized gas-ozone mixtureflows by pipe 149 to distribution means 105. The distribution meansincludes piping 151 that delivers the gas-ozone mixture to the soil insitu where it is further distributed by wells (not shown). Alternativelythe gas-ozone mixture flows by pipe 152 into pipes 153, 153A and then toone or both chambers 156, 156A, respectively that contain contaminatedsoil 154. Three way valve 150 may be used to discharge the off gas tothe proper pipe 151, 152 from pipe 149.

After passing through the soil in situ the stabilized gas-ozone mixtureis depleted completely or partially in ozone content. The gas may remaintotally or partially in the soil with no adverse effects as any excessozone will completely decompose in a few days or less. Any ozoneremaining in the gas-ozone mixture that reaches the surface of the soiland discharges to the atmosphere may be discharged as such or treated byozone neutralizer means (not shown). One method of neutralizationincludes the spreading of an ozone neutralizer over the soil. This isfurther discussed below.

After passing through contaminated soil 154 in chambers 156, 156A thegas-ozone mixture may also be partially or completely depleted of ozone.Pipes 157, 157A carry gas from the chambers to outlet pipe 163 fromwhich the gas may be vented directly to atmosphere through valved pipe159. If needed the gas can be piped to neutralizer means 164 by pipe163. Neutralizer means 164 neutralizes residual ozone in the gas priorto discharge to atmosphere at pipe 165. The neutralizer means 164 maycomprise an ozone quenching material such as Na₂ S₂ O₃ in a tank throughwhich a gas-ozone mixture is passed or as a blanket when soil is treatedin situ as further discussed below. Analyzer 162 may be used to analyzethe gas for ozone content through pipe 161. The design of analyzer 162is not critical and may be any known apparatus for determining ozonelevels as for example the use of KI solutions.

EXAMPLE 1

The stability of ozone in a soil environment was tested using acontinuous-flow column apparatus similar to that of FIG. 2 (columns 156,156A) except that an acidification unit (stabilizer means 104) fortreatment of ozone was not used. Shallow subsurface soil samples from 6to 18 inches deep were obtained from a location at West Jefferson, Ohioand used in the column tests. The soil type obtained was CrosbySilt-Loam. The characteristics are:

pH: 6.4 to 6.7

cation exchange capacity: 8 to 10 meq/100 g

organic matter content: 2 to 3 percent

Ozone was generated by passing pure oxygen (10 psi-gauge and 5 ft³ /hr)through an ozonator (Purification Science, Inc., Model LOA2). Theseconditions were maintained through all the experiments conducted in thepresent study. Concentration of ozone in the gas stream (ozone/ oxygenmixture) was measured by trapping the ozone in potassium iodide (KI)solutions and titrating the liberated iodine with sodium thiosulfate(Na₂ S₂ O₃); American Public Health Association, 1985, Standard MethodsDC. The average ozone concentration in the gas stream is 11.1mg(O₃)/g(O₂) with a relative standard deviation of ± 5 percent.

During these experiments, the ozone/oxygen mixture was passed through asoil column continuously for one hour. The column was about 6 cm deepand 4 cm in diameter for Examples 1, 2, 3, and 4. Gas leaving the columnwas analyzed for ozone content every ten minutes. The results presentedin Table I indicate that the ozone concentration in the ozone/oxygenmixture leaving the soil column (i.e. soil column off-gas) increasedduring the first 20 minutes and gradually decreased during thesubsequent 40 minutes.

                  TABLE I                                                         ______________________________________                                        Effects of Continuous Ozonation for One Hour on Off-gas                       Ozone Concentration.                                                          Ozonation Time                                                                              Off-gas Ozone Level                                             Minute        mg(O.sub.3)/g(O.sub.2).sup.a                                    ______________________________________                                        10            2.7                                                             20            3.3                                                             30            2.9                                                             40            2.4                                                             50            1.1                                                             60            0.77                                                            ______________________________________                                         .sup.a Each value is an average of two analyses.                         

EXAMPLE 2

Results of Example 1 show that the ozonation period may be inadequate toestablish the steady state conditions. Consequently, another test wasconducted to see how long it will take to reach the steady state and thecorresponding steady state ozone concentration in off-gas stream. Theresults of these experiments are presented in Table II. The steady stateozone level approached to undetectable levels after three hours ofcontinuous ozonation.

                  TABLE II                                                        ______________________________________                                        Steady State Time-Concentration Data                                          for Continuous Ozonation.                                                     Ozonation Time                                                                              Off-gas Ozone Level                                             Minute        mg(O.sub.3)/g(O.sub.2).sup.a                                    ______________________________________                                        15            5.3                                                             30            4.6                                                             45            2.1                                                             60            1.2                                                             75            1.0                                                             90            0.56                                                            105           0.5                                                             120           0.34                                                            180           ND.sup.b                                                        ______________________________________                                         .sup.a Results reported are average of two values.                            .sup.b Not detected.                                                     

EXAMPLE 3

Another set of experiments were conducted to investigate whetherintermittent ozonation (e.g. ozonation for a few minutes, leaving thecolumn without ozonation for some time and so forth) could improve theoff-gas ozone levels. Results presented in Table III show that suchintermittent treatment would not maintain high ozone levels in the soilcolumn off-gas.

                  TABLE III                                                       ______________________________________                                        Effects of Intermittent Ozonation on Off-gas Ozone Level.                     Treatment                                                                              Treatment Elapsed   Off-gas Ozone Level                              Type     Time, Min.                                                                              Time, Min.                                                                              mg(O.sub.3)/g(O.sub.2).sup.a                     ______________________________________                                        Ozonation                                                                              40         40       0.07                                             Oxygenation                                                                             5         45       .sup. NA.sup.b                                   No treatment                                                                           60        105       NA                                               Ozonation                                                                               5        110       0.2                                              Ozonation                                                                              10        120       0.14                                             Oxygenation                                                                             5        125       NA                                               No treatment                                                                           60        185       NA                                               Ozonation                                                                               5        190       0.36                                             Ozonation                                                                              25        215       0.11                                             ______________________________________                                         .sup.a Each reported value is average of 2 analyses.                          .sup.b Not analyzed (NA).                                                

Results from Examples 1, 2 and 3 indicate that soil ozonationby-products either exert increasing ozone demand or act asozone-decomposing catalysts. Since the extended or intermittentozonation did not result in higher ozone levels in soil column off-gas,it appears that ozone scavengers are formed during the soil ozonationprocess. Thus, long-term treatment of soils to remove contaminants withuntreated ozone is not feasible since the ozone decomposes too rapidly.The off-gas ozone levels further indicate that ozone penetration ofsoils is not adequate to assure decomposition of contaminants more thana short distance from the point of application.

EXAMPLE 4

If ozone scavengers are formed during the treatment process, theireffects may be reduced by pretreatment of soils or pretreatment of theozone gas stream. In this example, ozone gas was pretreated by passingit through a 5 percent HNO₃ solution (pH=about 0.1). The same soilsample used in Example 3 was treated for 45 minutes using acidifiedozone. This soil sample was selected assuming that it would give thegreatest amount of decomposition since it had been treated with ozonepreviously. The results are presented in Table IV. Acidification of thegas stream increased the stability of ozone so that ozone levels soilcolumn off-gas increased with time.

                  TABLE IV                                                        ______________________________________                                        Effect of Gas Stream Acidification on Off-gas                                 Ozone Levels in Small Soil Columns.                                           Treatment    Soil Column                                                      Period       Off-gas Ozone Levels.sup.a                                       (min)        mg(O.sub.3)/g(O.sub.2)                                           ______________________________________                                         0           0.11                                                             15           0.56                                                             45           6.5                                                              ______________________________________                                         .sup.a Average of 2 samples.                                             

An increase in the stability of ozone (O₃) in a soil environment can beexplained by two hypotheses: (i) the introduction of protons to soilscan reduce the formation of radical scavengers, and/or (ii) theformation of protonated ozone (O₃ H⁺) which is a more stable speciesthan O₃. These mechanisms are explained below.

Reaction of ozone with metal species in soils results in the formationof metal oxides. Some metal oxides can readily form their bases in thepresence of moisture. The hydroxide ions (OH⁻) generated during thisprocess greatly accelerate the decomposition of ozone. Highly reactivesecondary oxidants, such as OH. radicals, are thereby formed. Theseradicals and their reaction products further increase the decompositionof ozone; Hoigne, J., and Bader, H., 1976, The Role of Hydroxyl RadicalReactions in Ozonation Processes in Aqueous Solutions, Water Research,Vol. 10, pp. 377-386. In the present invention, addition of protons tothe ozone stream preferentially reduced the formation and/orconcentration of OH⁻ in the soil environment. Consequently, formation ofOH. will also be reduced. The net effect of all these reaction paths isto minimize the rate of ozone decomposition in soils.

Although not wishing to be bound by any theory, it is presently believedthat the mechanism of action is that, by acidifying ozone, anintermediate species of the formula O₃ H⁺, which is known as protonatedozone, is formed. Perhaps, protonation promotes the stability of cyclicozone. The role of protonated ozone in acid-catalyzed oxygenation ofalkanes with ozone in aqueous media has been explained in an article byYoneda and Olah; Yoneda, N., and Olah, G. A., 1977, Oxyfunctionalizationof Hydrocarbons, 7^(1a) Oxygenation of 2,2 - Dimethylpropane and2,2,3,3-Tetramethylbutane with Ozone or Hydrogen Peroxide in SuperacidMedia, Journal of the American Chemical Society, Vol. 99(9) pp.3113-3119; as an electrophilic insertion of O₃ H⁺ to form ahydrocarbon-O₃ H⁺ complex. In another article by Kausch and Schleyer;Kausch, M., and P. R. Schleyer, 1980, Isomeric Structures of ProtonatedOzone: A Theoretical Study, Journal of Computational Chemistry, Vol.1(1) pp. 94-98; molecular orbital calculations were used to determinethe structure of protonated ozone and four stable minima were found onthe O₃ H⁺ singlet potential energy surface. All four forms of protonatedozone are stable with respect to dissociation into O₃ and H⁺. Whateverthe mechanism, the advantages of the present invention are obtained bythe method herein where a gas-ozone mixture is passed through an acidprior to application to soil.

EXAMPLE 5

In the experiments conducted so far (Examples 1, 2, 3, and 4) the amountof soil used was only 300 g. Protonation of the ozone gas streamappeared to leave high levels of residual ozone (60 percent of incomingozone) after passing through 300 g of soil for 45 minutes. In order totest the effectiveness of protonation to treat large quantities of soil,further experiments were conducted using larger soil samples (up to 900g).

The experimental setup was modified to include two larger soil columns(6 cm in diameter and 40 cm in height) and a gas washing bottlecontaining 5 percent HNO₃ in the ozone influent line to the columns. Thetest unit is shown in FIG. 1. A continuous flow ozonation experiment wasconducted using 900 g of soil for 3 hour periods. The soil columnoff-gas was analyzed at 1, 2, and 3 hour time intervals.

When the ozone gas stream was first bubbled through an acid solution,higher ozone concentrations in the soil column off-gas were observedduring the three hour ozonation period (see Table V). The data alsoindicate that ozone concentrations were increasing gradually over thethree hour period. In order to achieve 6.6 mg (O₃)/g(O₂) in off-gasstream, it took about three hours for 900 g of soils whereas the off-gasozone level approached the same value in 45 minutes when the soil samplewas only 300 g (c.f. Tables IV and V).

                  TABLE V                                                         ______________________________________                                        Effect of Gas Stream Acidification on Off-gas                                 Ozone Levels in Large Soil Columns.                                           Treatment  Soil Column Off-Gas Ozone Levels                                   Period     at the End of Treatment Period                                     (hr)       (mg (O.sub.3)/g(O.sub.2)).sup.a                                    ______________________________________                                        1          1.8                                                                2          3.5                                                                3          6.6                                                                ______________________________________                                         .sup.a Average of 2 samples                                              

EXAMPLE 6

The preliminary investigations indicated ozone in a gas-ozone mixture,that was not subjected to acidification, was very unstable in soilenvironment. Ozone decomposed rapidly and the residual leaving a columnwith 300 g of soil decreased gradually (see Examples 1 through 3).Therefore, ozone that was not acidified was not expected to be usefulespecially for the treatment of larger quantities of soils. Thus, thesoil decontamination studies were conducted using acidified ozone whichwas more stable than untreated ozone.

A final set of tests involved ozone treatment of soils contaminated withphenol and 1,2,4-trichlorobenzene. Approximately 330 mg of phenol wasdissolved in 300 ml of acetone and thoroughly mixed with 1.5 kg ofsilt-loam soils to yield an approximate concentration of 200 ppm ofphenol in soil. The soil sample was air dried to remove acetone byvolatilization. Each glass column was packed with 740 g of phenolcontaminated soil. The compacted soil column was 21 cm high. One columnwas used in the ozonation experiment and the other was used as a controlwhere pure oxygen was used in place of the oxygen-ozone mixture. Thesoils were treated with the respective gases and soil samples wereremoved after 5, 15, 30, and 60 minutes from the initiation of theexperiments. Each sample was removed from upper 3 to 4 cm of the soilcolumn and weighed approximately 10 g. Soil was sampled from theuppermost layers since the decontamination is expected to be lowest inthis zone. All the soil samples, including one without phenol, weremixed with 30 ml of 90 percent methanol for phenol extraction. Phenolextracts were analyzed using high performance liquid chromatography(HPLC). This method is known to have a good linearity in the range from100 ppb to 100 ppm.

A stabilized oxygen-ozone mixture appears to be very effective inremoving phenol from soils. FIG. 3 generated from the chromatogramsshows that the passage of oxygen without ozone through the soil column(control experiments) did not result in a significant reduction ofphenol levels. In contrast, soils treated with the stabilized gas-ozonemixture had very low levels of phenol left after one hour of treatment.Removal of phenol by ozone at the uppermost soil layer where thedecontamination is expected to be the lowest was about 97 percent in onehour.

Stabilized ozone also was found to be effective for decontamination ofsoils containing halogenated organic compounds such as1,2,4-trichlorobenzene (TCB). In this set of experiments, a 30-cm soilcolumn was used. The TCB concentration in ozonated column was reduced by67 percent during 1.5 hour treatment. The fraction of TCB removal is lowas compared to phenol. Comparatively low TCB destruction can beattributed to its low reaction rate constant. The other reason could bethat the TCB soil column is larger than the phenol soil column.

The variation of soil column decontamination at different depths wasalso examined. After treatment with protonated ozone for 1.5 hours, theTCB levels were decreased by 84, 92 and 93 percent, respectively, atdepths of 5, 12 and 19 cm. These results show that the decontaminationefficiency gradually decreased with the increase in the distance fromthe source of ozonation.

Ozone, in the aqueous phase, reacts with a large number of organiccompounds. Some of these compounds include aromatics in general (e.g.benzene and hologenated benzenes, toluene, xylene, anisole, phenol,chlorophenols, and naphthalene), some unsaturated aliphatics (e.g.,ethylene, halogenated ethylenes, fumeric acid, and styrene), somesubstituted alkanes (e.g., ethanol, butanol, cyclopentanol, andacetaldehyde), and other compounds such as chloroform, bromoform,methylene chloride, and dioxane; Hoigne, J. and Bader, H., 1983, RateConstants of Reactions of Ozone with Organic and Inorganic Compounds - Iand II, Water Research, Vol, 17, pp. 173-183 and 185-194. Ozone preparedwith the method of the present invention will similarly react with thecited compounds.

The following discussion applies to field applications of the protonatedozone. Protonated ozone is to be applied to soils contaminated byaccidents or intentional release of hazardous organic compounds. Someexamples of unintentional releases or accidents include spills and leaksfrom underground storage tanks, pipelines, tank car derailments, etc.Intentional releases include field application of pesticides orherbicides and land disposal of hazardous organic wastes. For mostapplications in situ treatment is preferred over treatments requiringexcavation. The advantage of in situ treatment, when compared with otheron or off site treatment, is that soil does not have to be excavated,transported, or refilled. The in situ ozone treatment involves injectingof a stabilized gas-ozone mixture at pressures above atmosphericpressure into one or more injection wells in contaminated areas. Thedistribution of the well bank is to be determined by the effectiveozonation zone in the subsurface. The effective ozonation zone dependson the ozone concentration in the gas stream, pressure, flow rate,reactivity of the chemical with ozone, and soil properties such aspermeability, porosity, and organic matter content. Once knowing theteachings of the invention this can readily be determined by thoseskilled in the art. If desired, ozone that could be released to theatmosphere during this process can be trapped by using an ozoneneutralizing material such as sodium thiosulfate (Na₂ S₂ O₃) or thelike. One of the possible neutralizing means is the use of a spreadblanket wetted with Na₂ S₂ O₃ solution over the ozonation zone. If therelease of volatile organic matter is possible as a result of strippingaction, those compounds will be retained by a layer of activated carbonlying on top of the Na₂ S₂ O₃ wetted blanket. After the decontaminationprocess, if the soil is found to be too acidic, the pH may be increasedto a required level by applying unacidified gas-ozone mixture for sometime.

While the forms of the invention herein disclosed constitute presentlypreferred embodiments, many others are possible. It is not intendedherein to mention all of the possible equivalent forms or ramificationsof the invention. It is to be understood that the terms used herein aremerely descriptive rather than limiting, and that various changes may bemade without departing from the spirit or scope of the invention.

I claim:
 1. An apparatus for treating soil contaminated with organiccompounds comprising:a. an ozone generator adapted to receive an oxygencontaining gas from a gas supply means, that generates ozone from oxygenin the gas to produce a gas-ozone mixture; b. ozone stabilizing means,containing an acid, connected to the ozone generator by a first pipe forreceiving the gas-ozone mixture from the ozone generator, thatstabilizes the gas-ozone mixture by contacting the mixture with the acidto produce a stabilized gas-ozone mixture, wherein the acid has a pH ofabout (1) or less; and c. gas-ozone mixture distribution means,connected to the ozone stabilizing means by a second pipe for receivingthe stabilized gas-ozone mixture, that distributes the mixture to thesoil as a gas.
 2. The apparatus of claim 1 further comprising gas supplymeans connected to the ozone generator by a third pipe for supplying agas containing oxygen to the ozone generator.
 3. The apparatus of claim2 further comprising gas conditioning means adapted to purify and/orpressurize the gas, disposed between the gas supply means and ozonegenerator, wherein the third pipe connects the gas supply means to thegas conditioning means for supplying a gas containing oxygen thereto,and a fourth pipe connects the gas conditioning means to the ozonegenerator for supplying a conditioned gas containing oxygen thereto. 4.The apparatus of claim 1 wherein the gas-ozone mixture distributionmeans further comprises injection wells for treating the soil in situand fifth piping for distributing the gas-ozone mixture to the wells. 5.The apparatus of claim 4 further comprising:d. ozone neutralizing meansadapted to receive the gas-ozone mixture that has passed through thesoil and neutralize the residual ozone in the mixture, wherein the ozoneneutralizing means is a spread blanket wetted with Na₂ S₂ O₃ solutionover an ozonation zone.
 6. The apparatus of claim 1 wherein thegas-ozone mixture distribution means further comprises one or morechambers for treating the soil and sixth piping for distributing thegas-ozone mixture to the chamber(s).
 7. The apparatus of claim 6 furthercomprising:d. ozone neutralizing means adapted to receive the gas-ozonemixture that has passed through the soil and neutralize the residualozone in the mixture, wherein a seventh pipe connects an outlet of eachchamber to the ozone neutralizer means and neutralized gas is dischargedto atmosphere from the ozone neutralizer means.
 8. The apparatus ofclaim 1, wherein the ozone stabilizing means comprises a container withacid, and the gas-ozone mixture from the first pipe is bubbled throughthe acid to contact and stabilize the gas-ozone mixture, and thestabilized gas-ozone mixture flows to the distribution means by thesecond pipe.
 9. The apparatus of claim 1, wherein the ozone stabilizingmeans comprises a spray system for contacting the gas-ozone mixture fromthe first pipe and the stabilized gas-ozone mixture flows to thedistribution means by the second pipe.
 10. The apparatus of claim 1,wherein the acid is a strong inorganic acid.
 11. The apparatus of claim10, wherein the acid is selected from the group consisting of nitricacid, sulfuric acid, hydrochloric acid and mixtures thereof.